Semi-trailer trucks include a fifth wheel for towing a semi-trailer which includes a kingpin for connecting to the fifth wheel. It is often desirable for a semi-trailer truck, or a box truck, to tow one or more additional semi-trailers. A trailer converter dolly is commonly used to link one or more secondary semi-trailers to a leading semi-trailer or box truck. Alternaively, a dedicated full trailer having an integrated dolly may be linked behind a truck or leading trailer.Conventional trailer converter dollies and dollies of full trailers include a frame, a wheel axle assembly, wheels, and a fifth wheel commonly supported by a suspension mechanism. A drawbar assembly attached to the front of the frame often includes two individual bars that extend and converge away from the frame in what is commonly referred to as an A-shape configuration. Conventional drawbar assemblies typically have a fixed length and therefore maintain a towed trailer at a set distance behind a truck or other trailer. Such a set distance is typically large enough to allow maneuvering a trailer connected to the trailer converter dolly around tight corners, such as encountered in city driving conditions, without the trailer impacting the leading truck or trailer.
However, a problem with providing a space that permits such maneuverability is that the relatively large gap between the towed trailer and the leading truck or trailer reduces aerodynamic efficiency at highway speeds due to drag induced by a low pressure area formed between the towed trailer and the leading truck or trailer. Reduced aerodynamic efficiency reduces fuel economy, and is therefore undesirable. However, if the towed trailer is too close to the leading truck or trailer, the towed trailer will likely impact the leading truck or trailer when negotiating tight turns such as those encountered in city driving.
U.S. Pat. No. 5,338,050 discloses a trailer converter dolly that (1) provides a towed trailer with sufficient space to maneuver around sharp corners without impacting a leading truck or trailer and (2) reduces the gap between two trailers for travelling at highway speeds. The trailer converter dolly disclosed in the '050 patent describes a mechanism that requires stopping a truck to adjust the length of the drawbar. Once stopped, the mechanism withdraws a pin from a hole in the drawbar and the truck is moved to misalign the pin from the hole. A spring then urges the pin into contact with the drawbar, and as the truck continues to move the pin moves into the next hole in the drawbar. To make a further adjustment, the pin must again be removed from the hole it is in and the truck moved until the pin moves into the next hole in the drawbar.
The present inventor has recognized that the trailer converter dolly disclosed in the '050 patent has several disadvantages. One such disadvantage is that the tractor trailer must be stopped to adjust the length of the drawbar. Stopping a truck is time consuming and may be hard to accomplish because finding a place to stop a semi-tractor towing two or three trailers can be difficult. Another disadvantage is that the disclosed mechanism locks in each discrete position thus making it cumbersome to move the drawbar from its fully extended position to its fully retracted position. Another disadvantage is that the drawbar of the '050 trailer converter dolly includes two A-frame shaped bars. The present inventor has recognized that an A-shaped drawbar assembly increases the likelihood that the drawbar may impact the leading truck or trailer during tight maneuvering, and hinders access to the front of the towed trailer where an operator needs to access trailer hook-ups such as electrical connections and air lines.
The present inventor has thus recognized a need for a trailer converter dolly that automatically adjusts the distance between a towed trailer and a leading truck or trailer while the leading truck or trailer and the towed trailer are moving to provide clearance for maneuvering around tight turns and to reduce the gap between the towed trailer and the leading truck or trailer to reduce aerodynamic drag. The present inventor has also recognized a need for a trailer converter dolly that smoothly and easily adjusts a drawbar between a fully extended position and a fully retracted position, as well as a need for a trailer converter dolly that provides increased clearance from a leading truck or trailer and facilitates access to the front of a towed trailer.